[efi] Move architecture-independent EFI prefixes to interface/efi

Signed-off-by: Michael Brown <mcb30@ipxe.org>

diff --git a/src/arch/x86/prefix/efidrvprefix.c b/src/interface/efi/efidrvprefix.c
similarity index 100%
rename from src/arch/x86/prefix/efidrvprefix.c
rename to src/interface/efi/efidrvprefix.c

diff --git a/src/arch/x86/prefix/efiprefix.c b/src/interface/efi/efiprefix.c
similarity index 100%
rename from src/arch/x86/prefix/efiprefix.c
rename to src/interface/efi/efiprefix.c